1. Field of the Invention
The present invention relates to a technical field of polishing, and more particularly to a fixed abrasive polisher which can polish an object for a long period of time with high surface accuracy and without causing any damage during working, a process for producing the polisher, and a polishing tool using the polisher.
2. Description of the Related Art
Conventionally, in producing semiconductor devices such as DRAMs, other memories and microprocessors, predetermined circuit elements are formed on a surface of a semiconductor substrate, for example, a silicon substrate (a wafer), and insulating layers and wiring layers are formed on the surface of the silicon wafer to thus form a predetermined electronic circuit together with the above circuit elements.
In the production of such semiconductor devices, the steps of forming an insulating layer and a wiring layer, patterning the insulating layer and the wiring layer into a predetermined shape, further forming thereon an insulating layer and a wiring layer, and patterning the insulating layer and the wiring layer into a predetermined shape are repeated. Therefore, when forming the upper layer, the underlying surface begins to have irregularities formed thereon of a considerable level, and, in this state, an attempt to perform layer formation and patterning leads to the difficulty of forming a pattern having good uniformity in thickness and good shape.
In recent years, as the number of layers in multilayer wiring increases gradually, in order to solve the above problem, polishing is carried out to planarize the underlying layer, particularly a silicon oxide insulating layer, before the formation of the upper layer.
This polishing has hitherto been carried out by the so-called xe2x80x9cfree abrasive polishingxe2x80x9d in which a foamed polyurethane pad used for polishing glass and serving as a polisher is attached to the surface of a surface plate to form a polishing tool. Such a polishing tool is relatively moved while pressing the tool against the surface of an object to be polished (a silicon wafer with a layer formed on the surface thereof) at a certain pressure and, at the same time, while supplying a polishing liquid containing abrasive grains, for example, cerium oxide particles, thereby polishing the object.
According to this free abrasive polishing, however, it has been difficult to finish the surface of the silicon wafer having fine irregularities to a good flatness. This is because the foam polyurethane pad as the polisher constituting the polishing tool is relatively soft, and hence, it is difficult to obtain a desired flatness (surface accuracy).
Therefore, an effort has been made to improve the hardness of a polisher such as a foam polyurethane pad. Nevertheless, the free abrasive polishing cannot provide a sufficient surface accuracy.
On the other hand, Japanese laid-open patent publication No. 9-232257 discloses a polishing method in which polishing is performed with a polishing grindstone (a polisher) comprising abrasive grains such as cerium oxide bound in an organic resin material such as a phenolic resin. In this case, the polishing of an object is performed while supplying an abrasive slurry such as colloidal silica to a polishing tool comprising the above polishing grindstone attached to a surface plate.
The polishing method disclosed in Japanese laid-open patent publication No. 9-232257, however, uses a fixed-abrasive grindstone in combination with an abrasive slurry containing free abrasive grains. This polishing method produces a large quantity of waste liquid containing free abrasive grains, and thus, necessitates troublesome waste liquid treatment. In addition, the polishing method is liable to produce dust of abrasive grains contained in the abrasive slurry and mist containing the abrasive grains. Therefore, disadvantageously, measures should be taken to prevent the dust and mist from reaching the silicon wafer. Further, the combined use of the free abrasive grains and the fixed abrasive grains causes rapid wastage of the polishing grindstone, and thus, makes it difficult to maintain the surface accuracy of the polishing grindstone for a long period of time. Therefore, it is difficult to maintain a high surface accuracy of the polished objects for a long period of time. Disadvantageously, if it is contemplated that the high surface accuracy of the polished objects should be maintained for a long period of time, dressing should be frequently carried out to ensure the surface accuracy of the polishing grindstone.
It is therefore an object of the present invention to provide a fixed abrasive polisher which is free from the above problems involved in the use of free abrasive grains and can perform polishing of objects with high surface accuracy for a long period of time, and to provide a polishing tool using such polisher.
In order to achieve the above object, according to the present invention, there is provided a polisher comprising abrasive grains dispersed in a thermosetting resin, the polisher having abrasive grains of 20 to 60% by volume, a binder of 30 to 50% by volume, and pores of not more than 40% by volume.
According to one aspect of the present invention, the abrasive grains comprise at least one of cerium oxide, manganese oxide, titanium oxide, zirconia, silica, and iron oxide.
According to one aspect of the present invention, the abrasive grains have an average particle diameter of 0.01 to 2.0 xcexcm. According to one aspect of the present invention, the thermosetting resin comprises a polyimide resin or a phenolic resin. According to one aspect of the present invention, the Rockwell hardness is not less than 30 in terms of the H scale.
In order to achieve the above object, according to the present invention, there is provided a process for producing a polisher, characterized in that a mixture of abrasive grains and thermosetting resin particles is heated under pressure to mold the mixture into a desired shape.
According to one aspect of the present invention, the pressure is in the range of 9,800 to 49,000 kPa (100 to 500 kg/cm2). According to one aspect of the present invention, the heating temperature is in the range of 120 to 250xc2x0 C. According to one aspect of the present invention, abrasive grains comprising at least one of cerium oxide, manganese oxide, titanium oxide, zirconia, silica, and iron oxide are used. According to one aspect of the present invention, the abrasive grains have an average particle diameter of 0.01 to 2.0 xcexcm. According to one aspect of the present invention, thermosetting resin particles comprising polyimide resin particles or phenolic resin particles are used. According to one aspect of the present invention, the thermosetting resin particles have an average particle diameter of 0.1 to 20 xcexcm.
In order to achieve the above object, according to a further aspect of the present invention, there is provided a polishing tool comprising the above polisher mounted on a polisher holding member.
According to one aspect of the present invention, the polisher is mounted on the polisher holding member by an adhesive. According to one aspect of the present invention, the polisher has grooves on its surface. According to one aspect of the present invention, the polisher is mounted on the polisher holding member by mounting a plurality of polisher segments. According to one aspect of the present invention, the polisher is mounted on the polisher holding member by mounting a plurality of polisher pellets.